Add infrastructure for future DARC Community Logbook (DCL) integration:
- Database schema: Add dcl_api_key, my_darc_dok, darc_dok, dcl_qsl_rdate, dcl_qsl_rstatus fields
- Create DCL service stub with placeholder functions for when DCL provides API
- Backend API: Add /api/auth/dcl-credentials endpoint for API key management
- Frontend settings: Add DCL API key input with informational notice about API availability
- QSO table: Add My DOK and DOK columns, update confirmation column for multiple services
Note: DCL download API is not yet available. These changes prepare the application
for future implementation when DCL adds programmatic access.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
Joerg
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